Why is it an advantage that Mendel's discoveries were not sex-linked?

Case 1: Mendel's discoveries of the rules of inheritance benefited enormously from the fact that the genes he analysed were all on <u>diffrent </u>chromosomes and that there are <b><u>no</u></b> sex chromosomes in pea.

My lecturer said it was a big advantage!!! why so??

Case 2 : If neither of those conditions applied, what different results would it be??

My guess in case 2 is those genes in pea would be sex-linked and the phenotypic ratio would be 1 : 1: 1: 1 for different phenotypes, not 9 :3:3:1 like in case 1.

I don't get the significance of this difference between case 1 and 2.Anyone help to enlighten me please.[?]